FIG. 1 illustrates the constitution of the usual fluorescent indicator panel which is used as a digital indicator for displaying characters or symbols in the digital form in electronic meters, electronic calculators or communication apparatuses. This kind of fluorescent indicator panel is disclosed in Japanese Patent Publication No. Sho-54-41459.
The upper face of a base plate 9 which is made of an insulative material such as glass or ceramic is provided with functional layers such as: a wiring layer 10 forming a wiring pattern and made of a conductive material such as silver and the like; an insulative layer 11 made of a glass coating material including a black pigment and the like; a conductive layer 12 having a required pattern and forming an anode segment including a conductive ingredient such as graphite; and a fluorescent layer 13 made of a fluorescent material, the above layers being stacked in the cited order through printing technology and the like. Such a base plate 9 provided with the functional layers will be called "multilayer base plate" hereinafter.
A grid 14 for controlling emitted electrons in order to make the fluorescent layer 13 radiate is installed on the multilayer base plate, and a filament 16 for emitting the thermal electrons is installed by a filament supporter 17 fixed on the front and rear (or on the left and right) of the multilayer base plate. An envelope 15 playing the role of a front glass is attached in such a manner that the upper portion of the multilayer base plate should be surrounded, and thus, the conventional fluorescent indicator is completed by performing bonding, discharging and getter flashing and other required procedures.
However, such a conventional fluorescent indicator panel is capable of displaying the characters only on one side thereof, and if two sides are to be displayed, two panels have to be combined. Further, only a part of the heat produced from the filament can be utilized, and the rest of the heat is released to the envelope, thereby making the utilization of the heat insufficient. Further, in order to prevent the electrostatic charges in the envelope which has no special grounding means, an anti-electrostatic coating has to be carried out, thereby increasing the manufacturing cost.